Monday, August 30, 2010

We looked at some firearm myths last month. Now it is time to examine some more stories and see if they are really myths or true facts.

1. You can escape bullets by diving underwater.

We've all seen the movie scene where the hero swims underwater, while all the villains impotently shoot at the water in an attempt to hit him, but our hero emerges unscathed on the other end. Is this really possible, the reader asks. Well, there is a fair bit of truth to this. We've all seen people shooting into bottles filled with water and puncturing them with splashing all around. However, it is a different matter when one shoots into a larger body of water, such as a lake. Water offers a lot of resistance to bullet movement and slows down bullets considerably.

The popular TV show Mythbusters ran an episode where they tried to confirm or disprove this story. They rigged up a block of ballistic gel to simulate a human body and immersed it in a public swimming pool and then shot it with various weapons. One of the interesting things they noted was that slower moving snubnose bullets from a 9mm pistol seemed to penetrate deeper into the pool than faster moving spitzer bullets from rifles like the M1 Garand. In fact, faster moving spitzer bullets tumbled when they hit the water surface and quickly lost their speed. At certain angles, the bullets just disintegrated upon hitting the water surface.

They initially tried shooting a 9mm pistol vertically into a plastic acrylic tank containing water and a ballistic gel block and noted that the bullets lost enough speed that it couldn't penetrate the gel block below 8 feet (2.44 meters) of water when fired directly vertically in (which is the worst-case scenario). They then shifted operations into a bigger body of water, i.e. a local swimming pool.

In order to make things more realistic, they conducted the swimming pool tests by shooting at a 30 degree angle into the water surface (just as the guards might shoot at the hero escaping from the wall of the castle) and they discovered some surprising results:

Using a replica civil war rifle, they couldn't hit the block of ballistic gel from 15 feet (4.57 meters) or even 5 feet (1.52 meters) distance because the bullets kept swerving off in the water. When hitting it from a totally unrealistic 3 foot (0.91 meters) range, they managed to get a fatal penetration. Bear in mind that the gel was in only 2 feet (0.61 meters) of water for this to happen.

Using a modern day assault rifle shooting NATO 5.56x45 mm. ammunition, they tried shooting at the gel block from various ranges. Bear in mind that this weapon fires a bullet at 2500 feet/second (762 meters/second), which is way faster than a civil war era weapon. At 10 foot (3.05 meters) range, the jacketed bullet just shattered when it hit the water surface, with no fragments in the gel block. At 3 foot (0.91 meters) range, the bullet broke up as before, but the tip of the bullet just slightly penetrated the gel block in what would be a non-fatal injury.

Using an early 20th century M1 Garand rifle (which fires a bullet at 2800 feet/second (853 meters/second)) showed similar results. At 10 foot (3.05 meters) range, the bullet simply shattered on hitting the water surface and at 2 foot (0.61 meters) range, it barely penetrated the gel block.

They used a huge Barret 50 caliber rifle capable of shooting at over 3000 feet/second (914 meters/second). Bear in mind that this is a sniper rifle capable of long range shooting. Result: The bullets created a big splash upon hitting the water surface, but either disintegrated or lost enough momentum after travelling in 3 feet (0.91 meters) of water that they couldn't inflict a fatal wound to anyone below this depth.

Conclusion: This scenario could actually work if the person is deep enough under water, as water does decelerate bullets by a surprisingly huge amount. Also, faster moving spitzer bullets tend to disintegrate a lot quicker when they hit the water surface, depending on the angle and speed they're fired at.

2. You can fire a gun underwater.

Some readers may have heard of special forces using guns that can fire underwater and such. For instance, there is the Russian SPP-1 pistol invented for combat divers. The actual truth is that you don't need a special gun that fires underwater, because most modern ordinary weapons can also do so, but doing this is an extremely bad idea.

The first problem is that sound carries a lot further underwater, so if a person happens to be underwater when firing a weapon, it could rupture their eardrums and severely disorient them or even knock them out with the shockwave.

The second problem is if the barrel contains an air bubble when underwater, the bullet travels through it and then hits water. Since water isn't as compressible as air, the pressure spreads in all directions. At this point, with all the pressure building up, something has to give and usually it ends up with either the barrel or the action exploding.

The reason some people think that guns can't fire underwater is because black powder won't ignite when wet. Well, most modern weapons don't use black powder for their propellant. They use cartridges filled with modern propellants, which are capable of burning even when underwater.

So what happens if you clear the weapon of all air bubbles and then attach a thread so that the weapon fires underwater while the user stays out of the water (or at least with their head out). In this case, most modern weapons, such as a Glock or a SiG 9mm pistol will fire, as will rifles like an M-16 or a Garand M-1. However, the range of the weapon will be severely shortened because water tends to offer significantly more resistance to bullet movement, a fact that we already noted in our last section. A test by the Mythbusters TV show determined that an M-1 Garand bullet only had a range of around 6 feet (or less than 2 meters) when fired underwater. Also, the resistance of water also applies to the operating mechanisms of automatic and semi-automatic weapons. This means that these weapons will most likely not go through their operating cycles and hence will only fire one shot.

Conclusion: Yes it is possible, but it is an extremely bad idea.

3. You can come out of the water and start shooting immediately.

We've all seen scenes from Rambo movies where Sylvester Stallone's character suddenly pops out of the river and starts shooting people around him. So what's the truth here?

Like we noted in the previous section, water is not a very compressible fluid, so it is a good idea to get as much of it out of the barrel as possible before firing. If not, when the bullet hits the water pocket, it will try to push it out of the way and the water not being compressible is pushed with high pressure to the sides of the barrel. The barrel is usually not built to handle these levels of stress and may possibly explode. So, obviously, the key is to do one of two things:

Empty the barrel and action of as much water as possible very quickly, so it is possible to shoot the weapon. This means the barrel must have strategically placed drain holes to do this.

Make the barrel much thicker to handle higher pressures. However, this increases the weight of the weapon.

Both these methods are used by various manufacturers of modern Special Forces weapons. Examples of these would be Heckler & Koch HK-416, Magpul ACR, Robinson Armament XCR etc. In fact, there are videos of what is called the "Over the Beach" test that some manufacturers advertise, to show how quickly their weapons can be pulled out of the water and fired.

But recall that Vietnam Era special forces did the same thing with regular M-16s as well. So what did they really do? Well, the reality is that they had to clean their weapons and drain them out before using them. On leaving the water, they would point the barrel downwards and then pull back on the forward assist lever to break the tight seal in the barrel. This would allow most of the water to drain out. In fact, one of the early objections in the M-16s design was that the barrel was of 5.56 mm. diameter which meant more water would stay in the barrel due to capillary action, whereas a wider barrel would drain it quicker. That is why the field manual recommends against carrying the barrel upwards in heavy rain, otherwise water could get stuck in the barrel. The interested reader is welcome to read a now declassified report about the issues of the AR-15 (the prototype M-16) here: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD202468&Location=U2&doc=GetTRDoc.pdf. For those interested in how the procedure of draining water from the barrel of an M-16, chapter 2, page 0009 00-7 to page 0009 00-10 ("Unusual operating conditions") of the Army manual TM 9-1005-319-10 describes how it is done, along with pictures.

The new M16 Mark 4 Mod 0 has modifications to drain water from a barrel in around 8 seconds. This means it can start firing a lot quicker than its predecessors, but the user still needs to wait for water to drain first before firing. That means Hollywood is generally gassing when it shows people shooting the moment they come out of water.

There is also a secondary big movie myth here. Recall that the hero usually comes out of a muddy river and starts shooting immediately. Now a muddy river contains water, but also contains mud, silt, dead leaves, tiny fish, sticks etc., none of which is a good idea to have in a barrel when the shooting starts. In fact, it is a good idea to have nothing but air in the barrel before shooting. In Vietnam, special forces personnel would come out of the water and hide in a quiet place while they spent some time getting all the mud out of their weapons.

So what does a user who carries his weapon in the heavy rain do if he wishes to shoot immediately. First, one option as stated by training manuals, is to carry the weapon barrel downwards, so that rain water and other debris don't enter the barrel. Another option is to apply a condom at the end of the barrel. This keeps the water out and it is easily torn away by the first bullet coming through the barrel and doesn't affect its flight path that much either. In fact, there is a commercial product called a "barrel cot" that does exactly this and it is often used by hunters who hunt in snow or muddy conditions.

Sunday, August 29, 2010

In this post, we will recap all the stuff we've studied on blowback systems:

In blowback systems, the bolt is not locked when the gun is fired. This is the defining characteristic of all blowback systems.

All blowback systems use some of the gas generated when the cartridge is fired, to operate their mechanisms.

All blowback systems use the empty cartridge case as a sort of piston to operate their mechanisms.

The main problem to overcome on blowback systems is how to prevent the breech from opening the instant the gun is fired. The breech should only begin to open after the bullet has left the front of the gun and gas pressure in the chamber has dropped to a safe level. All blowback systems have different ways of overcoming this problem. Some use inertia, others use the principles of levers, still others use friction, gas etc.

So what are the advantages and disadvantages of such systems?

Advantages:

Blowback systems have fewer moving parts than other systems.

In most cases, there is no gas tube hanging off of one side of the barrel and affecting the natural harmonics of the barrel. This allows the barrel to be free-floated.

Generally reliable provided they are used with the ammo that they are designed for.

Relatively cheaper to manufacture.

Some blowback systems offer recoil reduction and less muzzle climb when firing rapidly.

Disadvantages:

Cannot be used with powerful cartridges. These are generally suited to low-powered or medium-powered weapons at most. This is why most blowback weapons are pistols or submachine guns, not high powered rifles.

Some actions (such as straight blowback) make the gun heavier by the nature of how they work.

Some blowback actions are extremely sensitive to the type of cartridge used. While they are reliable when used with the cartridge that they're designed for, slight variations (such as the weight or the material of the case) can cause problems. Unlike a gas operated system which has a user-tunable gas regulator, these cannot be tuned to different cartridges.

Some blowback systems quickly get dirty with use.

Blowback systems are generally most prevalent in smaller pistols and submachine guns, because they cannot reliably handle higher powered cartridges.

When a metallic cartridge is fired, the cartridge case expands slightly and seals off that side of the chamber and prevents gas escaping that way. Therefore, in all breechloading guns, the diameter of the firing chamber is slightly larger than the unfired cartridge case's diameter, so that the cartridges are easier to load. In a chamber ring delayed action, the back of the firing chamber has a ring around it on the inside, which makes the front of the firing chamber have a slightly larger diameter than the back of the chamber. So when the cartridge is fired, it expands to fill the chamber. However, since the front of the chamber has wider diameter, the front of the cartridge expands more than the back. Now when the cartridge is being pushed backwards by the expanding gases, the front of the empty case, which is now expanded to a larger diameter, rubs against the ring and slows down due to friction. Since the case is the one pushing the bolt back, slowing down the backwards movement of the empty case also delays the bolt motion correspondingly. This mechanism can usually only be used by really compact weapons, such as weapons made by L.W. Seecamp Co.

Seecamp LWS .32 ACP Semi-automatic pistol.

Image created by BillyTFried and used under the terms of GNU Free Documentation License version 1.2.

Off Axis Bolt

The next mechanism was invented by the famous firearms designer, John Browning. In this action, the motion of the bolt is not along the same axis as the barrel. Hence, when the bolt moves backwards, it moves along an inclined place placed at an angle compared to the barrel and thereby has more resistance to backward motion without increasing the bolt's weight correspondingly. This allows the weapon to have less recoil and less muzzle climb when firing in automatic. This mechanism was used in the 1938 French made MAS-38 submachine gun, has been used in some modern firearms as well, such as the US made TDI Vector submachine gun manufactured in 2009 and the Finnish Jatimatic submachine gun made in the 1980s. None of the firearms using this action have seen widespread popular use though.

Hesitation Locking

This is another design by the famous Danish-born US firearms designer John Pedersen, who we already encountered when discussing lever-delayed blowback actions. The Hesitation Lock action was designed by him when he was working for Remington and has only been used in one firearm model ever, the Remington 51 pistol, first made in 1917.

In this design, when the cartridge is fired, the empty cartridge case pushed back on the bolt, which causes the bolt to move backwards along with the slide. The cartridge case, bolt and slide initially all move back together for a short distance. Then the cartridge case and bolt stop moving because the bolt is stopped in place by a projecting locking shoulder, but the slide continues to move on backwards. This gap between the bolt/partially extracted cartridge and the chamber allows a little of the expanding gases to escape through the back, while most of it goes out through the front, along with the bullet. Meanwhile the slide continues to move on backwards and impacts a cam which rotates and releases the locking shoulder, which now allows the bolt and cartridge case to now freely move backwards. Meanwhile the bullet has already exited the barrel and most of the high pressure gas has also exited in that direction, so the pressure in the chamber has now dropped to a safe level. The empty cartridge case and bolt now continue backwards and the cartridge case is ejected via an ejection port. When the bolt goes to the maximum distance backwards, it is then pushed forward by the recoil spring and picks up a new cartridge from the magazine, just like a straight blowback action.

Due to the locking shoulder, this weapon can handle higher powered cartridges than a straight-blowback action. It also has lower recoil and less muzzle climb when firing. Remington also made the model 53, which used the same action, but was chambered for a .45 ACP cartridge. The Remington 53 had less recoil and muzzle climb and was deemed to have a simpler mechanism, lighter and more accurate than a Colt M1911 pistol, which was the standard sidearm of the US military at that time. However, when it came to getting a military contract, Remington wanted too much money up front and then World War I started and the United States military decided to continue with the M1911, since they already had a large investment in machinery and tooling for the Colt pistol. The Remington 53 never really found enough sales in the civilian market and so Remington went back to making the model 51, which they continued to do until 1928.

The history of the Advanced Primer Ignition mechanism started in the middle of World War I, where it was used for the Becker Autocannon (invented by Reinhold Becker) used on several German aircraft. It was later used in World War II in such guns as the MP-38, MP-40 and MP-44 and afterwards by Suomi M31, Uzi etc.

To understand the action, first we must realize that the word "advanced" has many connotations in the English language. However, the context in which "advanced" is used here is in the sense of "ahead of". So "Advanced Primer Ignition" must mean that the primer is ignited ahead of some other event happening. So what exactly happens here?

To answer that question, let us revisit what happens in a straight blowback action. In here, the cartridge is initially in the chamber and the bolt is holding it in place via spring pressure. When the user pulls the trigger, it releases a hammer, which strikes the back end of the firing pin at the end of the bolt. The front end of the firing pin strikes the cartridge, which then ignites the primer and propellant. The generated gases then push the bullet out of the weapon and also try to push the bolt backwards. However, since the bolt is much heavier than the bullet, it does not move right away because of inertia and only moves by the time the bullet has already left the barrel. The bolt then travels backwards along with the fired cartridge case, which is ejected in a side port. The backward moving bolt also recocks the hammer along the way and moves back till it reaches its backward-most position. After that, it is pushed forward by a spring and it picks up the new cartridge from the magazine on the way forward and pushes it into the chamber and it is now ready to fire the next cartridge. Such a mechanism is called a closed bolt because the bolt is normally holding the cartridge in place in the chamber before the trigger is pulled.

Now consider a slightly different mechanism. In this mechanism, the bolt is already held in its backward most position by a sear spring and there is no separate hammer. The bolt itself has a fixed firing pin. Such a bolt is called an open bolt because the chamber is open by default. When the trigger is pressed, the bolt is released and moves forward due to force from the spring in the back. On the way forward, it picks up a cartridge from the magazine and moves it into the chamber. When the cartridge is rammed into the chamber, the firing pin detonates it and the force of the explosion pushed the bolt back whereupon it moves back to the very back of the mechanism and is held in place again by the sear, ready to be fired again. Again, if the weight of the bolt is heavy, it will not move back immediately after the cartridge is fired, due to the inertia of the bolt.

Of course, in both these situations, the bolt is much heavier than the bullet to ensure that the bolt doesn't move back immediately after the cartridge is fired. Also, the cartridge is lower powered because if it was more high-powered, the bolt and recoil spring would need to be correspondingly heavier and therefore make the whole weapon impractical to use by most users.

Now imagine a slight variation of the open-bolt scenario we described above. What if the cartridge is ignited before it is fully pushed into the chamber by the bolt. In that case, the generated gas not only has to push the bullet out of the barrel, it needs to stop the forward momentum of the bolt completely before it can push the bolt backwards. This means the bolt is delayed from moving backward for a little bit more time. By the time the expanding gases start to push the bolt backwards, the bullet has already left the front of the barrel. This means that the bolt and recoil spring can be much lighter in this scenario than if it was using straight blowback. This is the advanced primer ignition method (i.e.) the primer of the bullet is ignited before the bolt has stopped moving forward completely.

Therefore, we answer the question posed a few paragraphs above: "advanced ignition" refers to the fact that the cartridge is fired in advance of being chambered fully.

In most submachine guns that use this principle, this effect is achieved by making the firing chamber's length very slightly shorter (typically, a few thousands of an inch) than the overall cartridge length. This causes the firing pin to ignite the cartridge a little before the bolt slams into the face of the chamber.

In larger caliber guns (such as some anti-aircraft cannon and anti-tank rifles), this effect is achieved by making an "extended" chamber (i.e. one that is longer than the cartridge length), which allows the cartridge to slide within the chamber and supports the cartridge during firing via the chamber walls. The cartridge often has a rim that is smaller than the overall diameter of the cartridge (vs. firearms using other principles, where the rim is usually the same diameter as the cartridge case), in order to allow the extractor to hook to it within the extended chamber.

There are some advantages to using API blowback. Because the bolt can now be much lighter, it makes the weapon easier to manage than one using straight blowback. API blowback also lessens the recoil as well as the muzzle climb of the weapon. The weight savings can be recycled to make a heavier barrel which means it can fire more powerful cartridges than a straight blowback action as well.

There are also some downsides to this action. The moment of ignition of the primer is more critical in API systems because if the primer is ignited too early (i.e.) before the cartridge is adequately seated in the chamber, the cartridge case could burst. If it is ignited too late, the weapon and cartridge case may be damaged, especially when firing higher velocity cartridges. Also, API blowback can only be used with open bolt weapons. Unfortunately, open bolt weapons are more inaccurate than closed bolt weapons, just by the nature of how they work. API blowback also makes the weapon very dependant on strength of cartridge, weight of bolt, length of chamber and rate of fire. In an API blowback design, the variables "rate of fire" and "muzzle velocity" are generally mutually exclusive of each other, so if you want a high rate of fire, the muzzle velocity of each bullet must be slower and vice versa.

In our last few of posts, we've studied the basic principles of a blowback action and the reason why we want to delay the blowback action. In our last couple of posts, we saw that mechanical means can be used to delay the movement of the bolt, as well as a method that uses friction. In this post, we will look at another way to delay the movement of the bolt -- a method that uses some gas from the cartridge to delay opening the bolt, the Gas Delayed Lock.

In a Gas Delayed lock (as opposed to a gas operated weapon), when the cartridge has just been fired, the case of the fired cartridge tries to push the bolt backwards (all blowback pistols have a common property that the bolt is not locked at the moment of firing). However, some of the gas generated by the cartridge is bled off to a separate chamber that contains a piston and a spring. This piston offers extra resistance to the movement of the bolt and does not allow the bolt to move immediately. This allows the bullet to exit through the front of the barrel, taking most of the high pressure gas out of the chamber via the same exit. When the pressure in the chamber drops sufficiently, the bolt is now free to move backwards.

Public domain image. Click on image to enlarge.

In the above example, there is a hollow cylinder under the barrel which has a piston in it. The other end of the piston is attached to the front end of the slide. When the cartridge is fired, the gas pressure acts on the bullet and pushes it out of the barrel. The pressure also acts on the fired cartridge case, which attempts to move backwards and push on the bolt. However, some of the gas in the chamber is siphoned off and enters the cylinder underneath the barrel and pushes upon the piston. Since the other end of piston is attached to the front end of the slide, the slide now has two forces acting upon it: a force acting on the empty cartridge case that is trying to push it to the right, and a force acting on the piston, trying to push the slide to the left. As a result, the slide and the bolt don't move much at all. When the bullet exits the barrel, most of the high pressure gas leaves via that exit and the lower cylinder loses its pressure as well. As a result, the slide and bolt can now move backwards by momentum. This opens the breech and ejects the fired cartridge case.

The first use of this mechanism in a weapon was in the Volksturmgewehr 1-5 ("People's Assault Rifle"), also known as the VG 1-5. It was designed in 1944 by Karl Barnitzke towards the end of World War II, to be used by the Volksturm (a.k.a. "People's Militia"), which was a secondary force consisting of people in Germany between 16 and 60 years old, who were not already serving in the military in World War II. This weapon was designed to be cheap and easy to produce and used some parts in common with the StG 44 assault rifle.

The Barnitzke design was later used in the Swiss W+F 47 prototype pistol, the Steyr GB pistol, the Heckler & Koch P7 pistol and the Norinco M-77B pistol. In the case of the Norinco pistol, the M-77B is a bigger version of the M-77 and uses a bigger round. The gas delayed blowback system allows it to reduce the recoil of the weapon.

Sunday, August 22, 2010

In our last few of posts, we've studied the basic principles of a blowback action and the reason why we want to delay the blowback action. In our last couple of posts, we saw that mechanical means can be used to delay the movement of the bolt. In this post, we will look at another way to delay the movement of the bolt -- a method that uses static friction, the so-called Blish lock. The Blish lock is used in one of the most famous weapons invented in the early 20th century, the weapon that gave rise to the term "submachine gun", the one and only Thompson submachine gun, a.k.a the "tommy gun".

The Blish lock was invented by John Bell Blish, a career officer in the US Navy. While he was serving aboard a US Navy warship, he noticed a very interesting fact about naval guns. The guns in question were breech loading with screw on type breech blocks. He noticed that if a gun was fired with a normal round with a full load of gunpowder, the breech block would hold in place perfectly, but if it was fired with a training round which has a lot less gunpowder in it, the breech block would tend to unscrew itself and the case would fall out. After a lot of analysis about this phenomenon, he came to the conclusion that certain dissimilar metals tend to stick to each other if very high pressure is applied. This principle of metal-to-metal adhesion is now known as the "Blish principle." This adhesive force is really due to static friction between the two metallic surfaces. While he was not entirely certain about the physics behind the phenomenon, he did nevertheless note down that it happened and applied it to designing a wedge shaped blowback action that he patented in 1915. The action consisted of two diagonally sliding dissimilar metal wedges on the back of the bolt. Due to the pressure of the gases and the Blish principle, these two metals would adhere to each other initially. This extra resistance slows down the backward movement of the bolt. It was noticed much later that the Blish lock was not as effective as proclaimed, and the same effect could be obtained by merely increasing the weight of the bolt by one ounce and making it work on the principle of straight blowback.

While the Blish lock patent itself went nowhere initially, the next development came due to a retired US Army General, John T. Thompson, and the onset of World War I. The standard US military rifle at that time was the venerable bolt action M1903 Springfield rifle and the standard pistol was the Colt M1911. Interestingly, Gen. Thompson had earlier served as the chief of the Small Arms Division of the Ordinance department and had supervised the development of the Springfield M1903 rifle and approved the selection of the Colt M1911 pistol.

During World War I, trench warfare became the standard method of fighting and it became clear that there was a need for a weapon with a high rate of fire that could be used to clear a trench of enemies. General Thompson was looking to replace the bolt action rifle with an auto-loading one, a concept he called the "trench broom." He was aware of gas operated and recoil operated actions in his day, as these were in use for medium and heavy machine guns, but these used many heavy moving parts and were not as reliable then. He researched the straight blowback actions of the day, which were only suitable for really low powered ammunition. While he was studying various blowback actions, he came across the Blish patent and decided to use it instead. Accordingly, he arranged a meeting with John Blish and offered him some stock in the new weapons company he was planning to form, in exchange for the manufacturing rights of the Blish patent.

With Blish as a partner, Thompson secured some venture capital and formed the Auto-Ordnance Corporation in 1916. He also managed to hire Theodore Eickoff, who was once Thompson's assistant when he was running the Army Ordnance department. He also found an unemployed railroad fireman with mechanical aptitude called George E. Goll and hired him to be Eickoff's assistant. These two men were the principal designers of the Thompson submachine gun. Later on, Oscar Payne also joined and added some key Tommy gun features, such as the self-oiling mechanism and its distinctive drum magazine.

The original plan was to develop an auto-loading rifle using the military .30-06 round, which is the same round that the Springfield M1903 rifle uses. However, a series of problems were discovered with the Blish lock. For one, it could not handle such a powerful round and would wear out prematurely. Worse, the extraction of the fired cartridge case would not work unless the cartridges were lubricated. Eickoff did some research and found that the only military cartridge that would work reliably with the Blish lock was the .45 ACP cartridge, which is the cartridge used for the Colt M1911 pistol. Eickoff dreaded telling Thompson the bad news, but to his surprise, Thompson took the news very well and said "Very well, we will put aside the rifle for now and instead build a little machine gun. A one-man, hand held machine gun. A trench broom!" Thompson had realized what many European generals of the era hadn't, that nineteenth century warfare tactics didn't mix very well with twentieth century weapons. The traditional cavalry offensive charge was no match for heavy machine guns in trenches and the war had stalled with heavy casualties and little progress. While machine guns of the day were great for defense, they were too large and too heavy to be used for offensive actions. What Thompson visualized was a hand-held weapon with enough firepower, that could be used for hit-and-run tactics to clear enemy trenches. Accordingly, he directed Eickoff to develop a class of firearms that had never existed before then.

By the summer of 1918, all problems had been solved and the new class of weapon was called the "Annhilator Mark I". The first batch of weapons destined for Europe was delivered to the New York harbor on November 11th 1918, the very day that the armstice was signed in Europe, signalling the end of World War I. Suddenly, Thompson was stuck with a weapon that didn't have any demand! However, he was not a man to be let down by this setback and directed Auto Ordnance to redesign it for civilian use, which they did by 1919. Seeking a new name that could be used to distinguish it from its larger and heavier machine gun ancestors, he came up with names like "Autogun" and "Machine pistol", before coining the term "submachine gun". The rest, as they say, is history.

Two views of the Blish lock (note the brass content). Note the wedges along the center and the sides of the H shaped lock.

Bolt, Blish lock and actuator of a Tommy Gun. Note the dissimilar metals used

Disassembled Blish Lock, Bolt and Actuator

Tommy Gun with straight box magazine

Tommy Gun with rotary drum magazine

The Tommy gun was initially marketed to the police. The improved model M1921 was also offered for sale to the general public. It was a very finely machined weapon with high quality components and consequently commanded a high sale price of $200 (for contrast, a Ford car of that era cost only $400). It really came into the public eye during the Prohibition era, when both gangsters and law enforcement began to heavily use it. It acquired such nicknames as the "Tommy Gun", "Chicago Piano", "Typewriter", "Chicago Typewriter", "Chopper", "Broom" etc. Due to its notoriety, it was the main reason for the passage of the National Firearms Act of 1934 in the US. It was also used by the US marines in several smaller conflict and was adopted by the US military in 1938. It was used in World War II, Korea, Vietnam and beyond. It still turns up in some present day conflicts occasionally, such as the Bosnian war of the 1990s.

Image taken from wikipedia.org, uploaded by user Hmaag under a Creative Commons Attribution-Share Alike 3.0 license.

The bolt of this weapon has a hinge joint attached to the middle of it. The back of the crank is attached to a rear of the receiver via a fixed pin. Initially, the crank is at a near horizontal position. When the cartridge is fired, it pushes back on the bolt, which in turn applies its force to the front part of the crank. At this point, the crank pivots upwards until is is nearly vertical and provides significant mechanical resistance to the backward movement of the bolt because of the mechanical disadvantage applied. This resistance is enough to delay the movement of the bolt until the bullet has left the front of the barrel, along with most of the high pressure exhaust gases. When the crank reaches its near vertical position, the resistance to backward motion significantly decreases and the bolt can now move backwards. The empty cartridge case follows the bolt and is ejected via a side port. The bolt moves back and recocks the weapon automatically. When the bolt reaches the rearmost part of its travel, it is pushed forward by the recoil spring at the end. The bolt moves forward and picks up another cartridge from the magazine and it is now ready to fire.

This mechanism was used in only a couple of weapons: the Schwarzlose machine gun and the Pedersen rifle, designed by noted American designer John Pedersen.

The above image is a patent application by John Pedersen for his Pedersen rifle.

When we think of the words "mechanical advantage", the first object that many of us think about is the simple lever. We use a straight rod as a lever, balance it about a fixed pivot (fulcrum) and place the heavy object under the short-end of the lever. We then pull on the long end of the lever. Since we're pulling on the long end, we don't have to apply as much force, but we have to move the lever through a longer distance to move the object a short distance.

Conversely, if we put the object on the long end of the lever and push down down the short end, we put ourselves at a mechanical disadvantage and need to apply a lot more force to move an object. However, pushing down a small distance on the short end will move the object a lot more on the long end.

This is the principle of the lever-delayed blowback action.

Click on image to enlarge and view the animation in all its glory.

The original image disappeared from the web around May 2013. Luckily I was able to restore it from backup.

In the above image, we have a pretty good animation of how the lever-delayed action works. When the cartridge is fired, the rear movement of the spent cartridge case (the yellow part) acts upon the blue bolt. Before the bolt can move much though, the gray lever rotates and moves the red bolt carrier first, which moves a long way for the short movement of the bolt (the leverage principle we just talked about above). This leverage acting on the bolt carrier increases the force of resistance to movement and slows down the movement of the bolt itself. Once the lever has reached an approximately horizontal position, it ceases to act as a lever and the bolt and the bolt carrier move backwards together at the same speed and are followed by the empty fired cartridge case as well. This extra initial delay in the movement of the bolt serves to keep the gas seal fairly tight until the bullet has left the front end of the barrel and most of the high pressure gases have also gone out the front.

The picture above shows the drawing of an actual weapon (a French FAMAS assault rifle) that uses the lever delayed blowback action. Initially, the cartridge J is in the breech and the hammer H is cocked. When the trigger is pulled, the hammer H releases and strikes the back of the bolt A and the long firing pin E, which strikes the base of the cartridge J, igniting its primer and burning its propellant material. As the bullet begins to leave the front of the barrel, the empty cartridge case J now pushes back on the bolt A, which in turn transmits the force to lever B. The lever B rotates about the pivot C and moves the bolt carrier D faster than the bolt A. Due to this leverage being applied to weight of D, extra force must be applied to A initially to move it. As long as B is rotating, bolt A moves backwards a lot slower than D and therefore the breech stays practically shut. Once B has reached a horizontal position, it ceases to act as a lever and then both A and D move backwards at the same rapid speed, opening the breech. The case J also follows A backwards and is ejected out of a side port due to a spring inside the magazine that is pushing new cartridges upwards. The backward movement of A also compresses a recoil spring in the tube G and also cocks hammer H on the way back. The sear spring mechanism F holds down the hammer H after it is cocked and while the bolt is moving backwards. The bolt moves backwards, continuing to compress the spring G, until it is slowed down to a stop by G and the additional lever and spring K at the back of the weapon. These two then push the bolt forward whereupon it picks up the new cartridge from the magazine and moves it forward into the chamber.

Since this action uses the principle of leverage between A and D, the weights of A and D can be relatively light, since the leverage is what provides the resistance to backward movement of the bolt. This means the weapon can be much lighter than one that is using a straight blowback action. Conversely, the weight savings gained from the lighter action can be re-used to make a heavier barrel and chamber and therefore it can fire a much more powerful cartridge than a straight blowback weapon.

The first lever-delayed blowback action was invented by the famous Danish born US firearms designer, John Pedersen. However, it was perfected by the noted Hungarian firearms designer Paul Kiraly in the 1930s. This action is not used in many weapons, but the most famous current user of this action is the French FAMAS assault rifle.

French FAMAS F1 assault rifle

The FAMAS itself was heavily influenced by the mechanism of the French AA-52 LMG, which was developed after the 1950s and also uses a lever delayed blowback action. The FAMAS is significantly lighter than most assault rifle weapons of its class. Other users of this action include the Dominican Republic San Cristobal 0.30 carbine (designed by Paul Kiraly after he fled Hungary during the communist revolution and settled in the Dominican republic) Brazilian BSM/9 M1 submachine gun, the Italian Benelli B76 pistol and a series of Russian firearms designed by Anatoly Baryshev (AB-7.62, AVB-7.62, LCZ B20).

As an interesting side note, there was also a Soviet assault rifle called the TKB-517 that was developed in the 1950s by a Russian firearms designer named German A. Korobov. Mr. Korobov initially experimented with various assault rifle designs using gas delayed blowback operation throughout the late 1940s. While his earlier attempts were accurate enough, they were not as reliable and therefore, he switched to using a Paul Kiraly designed lever delayed action in 1952, which gave him better accuracy as well as better reliability. In the mid 1950s, the Soviet military decided that they needed to replace the original AK-47 assault rifle with a better design and opened a competition to develop a replacement. The TKB-517 rifle was submitted to the competition against a modified Kalashnikov AK-47 and some other competing designs. The TKB-517 was found to be the most accurate and controllable of all the designs submitted, especially in fully automatic fire mode. It was also much lighter and cheaper to manufacture than even the modified AK, which is quite an achievement in itself. However, the Soviet military decided that the less accurate, more expensive, but familiar and already well established Kalashnikov design was preferable to the more accurate, cheaper, lighter, but newer design TKB-517 and hence, the winner of the competition was declared to be the Kalashnikov designed modified AK, the AKM, which is the most widespread assault rifle in history.

Thursday, August 19, 2010

In our previous post, we studied the basics of the blowback action and learned a few things.

Blowback actions do not have the bolt locked in place at the moment of firing. Instead the bolt is held in place by inertia and springs.

When the cartridge is fired, it is desirable for the bolt mechanism to only start moving backwards after the bullet has left the front end of the barrel and the gas pressure in the chamber has dropped to a safe level. This is because: (a) a tight gas seal must be maintained until the bullet has left the barrel for greater range. It wouldn't do to leak gases out of the back end and reduce the pressure in the barrel while the bullet is still inside the barrel (b) It is not good for high pressure gas to blow through the magazine area and out the ejection port and rearrange everything inside the gun on the way out.

Therefore, there must be some method used to delay the backward movement of the bolt after the cartridge is fired.

As we saw in our previous post about straight blowback actions, one way to achieve this is to use a bolt that is much heavier than the bullet and use a stiff spring to hold the bolt in place. That way, when the high pressure gas acts on the bolt, it does not move much right away because of inertia. By the time the bolt and fired cartridge case start moving backwards, the bullet has already left the front of the barrel along with a lot of the high pressure gas, the pressure inside the chamber has already dropped to a much safer level and the bolt and cartridge case are moving back mostly due to momentum. Unfortunately, this makes the weapon much heavier than normal and harder to cock initially, as the user has to apply much more force to move a heavier bolt and stiff spring. Therefore, weapons that use straight blowback tend to use smaller and low powered cartridges to be suitable for practical usage by normal users.

Another alternative is to develop some kind of mechanism where the bolt encounters some higher resistance when initially trying to move backwards. This ensures that the bolt is delayed from moving backwards immediately after the cartridge fires and it doesn't move until the bullet has left the barrel. The idea is to put the bolt under some kind of mechanical disadvantage, so that much more force is required initially to move the bolt backwards. With such a mechanism, there is no need for a heavier bolt or stiffer spring and therefore the whole weapon can be lighter. Conversely, the weapon can also fire higher powered cartridges since the weight savings gained by a lighter bolt can be used to make the barrel heavier and breech mechanism stronger.

One way to do this is to use rollers to delay the bolt. Such an action is called roller delayed blowback. The most well known weapons that use this action are the Heckler & Koch G3 rifle and the Heckler & Koch MP-5 submachine gun.

The history of this type of action dates back to the middle of WW-II when it was used for an MG42 derivative and the Mauser StG 45. After the war, Mauser's factories were taken over by the French government and reorganized under a French organization called CEAM. Two of the former Mauser engineers, Dr. Ludwig Vorgrimler and Theodor Loffler were employed by CEAM and together perfected the roller delayed blowback design. Although they perfected the design based on the Mauser StG 45 cartridge (7.65 x 35 mm.), the French military then wanted to use a US designed .30 cartridge instead and so they were told to redesign for the new carbine. The French government also got involved in Vietnam by 1949 and therefore cancelled the project for lack of funding. Dr. Vorgrimler later left CEAM in 1950 and went on to join the Spanish company CETME, where they had already recruited some other former Mauser workers, as well as some others from another major German weapons manufacturer from world war II, Rheinmetall GmBH. Therefore, it was CETME that released the first commercial rifle using roller-delayed blowback, rather than CEAM. The post-war West German government was interested in the CETME design and licensed it for manufacture by Heckler & Koch and Rheinmetall. The result was the development of the Heckler & Koch G3 rifle. Dr. Vorgrimler was later employed by Heckler & Koch in the 1960s and went on to develop many more successful designs including the MP-5 submachine gun, which is still used by many forces worldwide.

The principle of the roller delayed blowback is to use two small masses (i.e. the rollers) usually attached to the bolt and arranged so that they move at nearly right angles relative to the bolt, at the moment of firing. The roller mechanisms act like levers and effectively multiply the mass of the bolt and bearings, which means that greater force is required to move them. The extra mechanical work that must be done to overcome this force generally allows the pressure in the barrel to fall to a lower level by the time the bolt starts to move backwards and thus delays the motion of the bolt until the bullet has left the barrel and the pressure has already dropped to a lower level.

The roller-delayed blowback mechanism of a Heckler&Koch G3 rifle. Public domain image.

US Patent 3283435. Drawing of roller-delayed blowback mechanism

When the weapon is cocked, the rollers (5a and 5b in the patent drawing) lock into the recesses in the trunnion (7a and 7b) and the face of the bolt head (4) sits flush against the base of the barrel, providing a tight seal. When the cartridge is fired, the bolt tries to move backwards and forces the two rollers (5a and 5b) against the locking piece (2). The locking piece, in turn, pushes against the bolt carrier (1) and the spring locking lever. The rollers act as levers and effectively multiply the mass of the bolt, which increases the force needed to push the bolt back. Once the rollers are pushed out of the trunnion recesses and are inserted back into the bolt head, the whole bolt assembly can now move backwards much easier. The bolt then moves back against spring pressure from the recoil spring (10) and the empty cartridge case can be extracted and ejected out of a port on the side of the weapon. When the bolt moves backwards to its maximum position, the recoil spring then pushes the mechanism forward whereupon, it picks up the next cartridge to fire from the magazine and loads it into the chamber.

The next figures from hkpro.com also make the concept very clear.

As the bolt head moves backwards, the force is transmitted from the bolt head to the rollers, as indicated by the horizontal red arrows. The rollers in turn, split the forces to the barrel extension and the locking piece, as indicated by the other red arrows. Approximately 75% of the force goes to the barrel extension and only 25% to the locking piece.

The extra force that is need to push the rollers out of the recesses and back into the bolt delays it enough for the bullet to leave the barrel and take most of the high pressure gases out of the front of the barrel. As a result, by the time the bolt starts moving backwards, the pressure of the gases in the chamber have dropped to a much lower level.

Image taken from hkpro.com. Unfortunately their web-server keeps going up and down, forcing me to not link to them directly.

In the above figure you can see the position of the rollers from where the bolt is in a locked and unlocked position. Once the rollers have moved out of the trunnion recesses, the whole bolt assembly moves back easily, just like in a straight blowback system; and the empty cartridge case moves back with it and is ejected out of the receiver.

There are some advantages and disadvantages of a roller delayed blow back system.

Advantages:

The barrel can generally be free floated, since there aren't any moving parts up front. This is unlike a gas operated mechanism, where part of the mechanism is hanging off one side of the barrel and disturbing the natural harmonics of the barrel. Free floating the barrel increases the accuracy of the weapon.

Unlike the straight blowback mechanism, this one can use higher powered ammunition.

When used with suitable ammunition that is designed for the weapon, this is a pretty reliable design.

Moderately cheap to manufacture.

Disadvantages:

This design definitely doesn't like wide varieties of ammunition. It is sensitive to factors such as the weight of the bullet or the type of case. Therefore, the ammunition used for this weapon needs to be good quality and manufactured to uniform standards, otherwise it could cause operating issues.

This is a design that can get dirty very quickly while using. It is fairly easy to clean up though.

It is a relatively complex system compared to some other designs, such as the AK-47 mechanism.

The locking delay can go down as the parts begin to wear out, chamber gets dirty or clean etc.

Cannot be tuned by a user, unlike a gas-operated mechanism with a regulator is.

Though CETME invented the first commercial rifle using this action, Heckler & Koch are the best known users. Several Heckler & Koch products such as the G3 rifle, MP-5 submachine gun, P9 pistol, HK-21 and HK-23 machine guns, SL-6 and SL-7 hunting rifles all use this mechanism. Other users of this action include the Swiss SIG SG 510 rifle and CETME rifles such as the modelo A, B, C, L and LC .

Wednesday, August 18, 2010

The blowback action is one of the more common actions used in modern firearms today. It is mostly seen in smaller caliber automatic and semi-automatic weapons such as the Uzi, Sten gun, Ingram MAC-10, Walther PP series (the Walther PPK is usually what fictional spy James Bond usually uses), Makarov etc. Actually there are many different systems that utilize variants of the blowback principle, so the next few posts will be devoted to studying these many variants.

The main principle behind a blowback action is that, at the moment of firing, there is a block of metal called a "bolt" that holds the cartridge in place. This bolt is not locked down, but is held in place by spring pressure. This is a very important point and is the main feature of a blowback action. When the cartridge is fired, the bullet flies out via the barrel and the expanding gases also push against the cartridge case which is still in the barrel. The cartridge case acts somewhat like a piston and in turn pushes on the bolt, which then moves backwards and recocks the weapon. At about the same time, an opening on the top or the side ejects the old spent cartridge case.

The following diagrams will make the concept clear.

In the above figure, we have the bolt in blue. The bolt handle A is used to pull the bolt backwards initially against spring pressure from recoil spring B. This moves the whole bolt (the blue piece) backwards. C is a cavity in the bolt, where hammer E (in rose color) can move). D (in red) is the firing pin. When the gun is initially loaded, a magazine containing cartridges is first inserted into the weapon. Then, handle A is used to pull the bolt back as shown in the figure above. As a result of this, the hammer E rotates about its axis and is cocked. At the same time, due to the pressure of magazine spring F, a new cartridge is pushed upwards into the receiver. When the bolt handle A is released, the front face of the bolt (the blue part) pushes the cartridge forward so it is pushed into the chamber in front of barrel H. The hammer E still remains in its near horizontal position because it is held in place by the trigger bar (which is orange) connected to trigger G.

Now the user pulls the trigger and the following happens:

The user pulls the trigger and the trigger bar releases the hammer E, which rotates about its axis inside cavity C and strikes the firing pin D hard. The other end of the firing pin strikes the base of the centerfire cartridge, which detonates its primer and then ignites the main propellant material in the cartridge. The expanding gases drive the bullet through the barrel H and also push back on the empty cartridge case left behind in the chamber, which in turn pushes back on the bolt.

The entire bolt assembly (the blue part) now moves backwards due to the pressure from the gases acting on the (now-empty) cartridge case. As a result of the bolt moving backwards, the hammer E is now rotated back down until the orange trigger bar holds it down Meanwhile, the opening on top of the receiver is now open and the old cartridge case is pushed out through here by the action of magazine spring F. The bolt moves backwards and compresses the recoil spring B. When the bolt has moved backwards to its utmost, the recoil spring B then expands and pushes it forward into place. While moving forward, the bolt picks up the new cartridge and pushes it into the chamber and the gun is now ready to fire again.

Obviously, for best results, the bolt should not start to move backwards before the bullet has left the barrel and the pressure in the chamber has dropped to a safe level (you don't want a lot of high pressure gas to flow back into the magazine area and out the ejection port and blow out everything in between). In a straight blowback action, this is achieved by making the bolt much heavier than the bullet mass. Therefore when the cartridge is first fired, the bullet shoots out the barrel, but the force acting on the empty case doesn't push the bolt back instantly due to its inertia. By the time the bolt starts to move backwards, the bullet has left the barrel already and pressure of the gas in the chamber has already dropped to a safe level and the bolt and empty cartridge case are moving back on pure momentum alone. Given the larger mass of the bolt and the stiff recoil springs, blowback weapons are usually a bit harder to cock initially. That is why, for most practical purposes, blowback weapons generally tend to use smaller and lower powered ammunition.

The following video shows a MAC-10 submachine gun, which uses a straight blowback action.

And now, a girl firing a Walther PPK pistol. Notice in the beginning of the video about 10 seconds in, when she loads the pistol and pulls the slide back the first time to cock it.

As we alluded to above, in a straight blowback action, the bolt assembly has to be heavy so that it doesn't move back the instant the cartridge fires. As a result of this, straight blowback weapons tend to be heavier than other similar sized counterparts that use different mechanisms. Some manufacturers, such as Hi-point Firearms, try to get around this by making the other parts of the weapon out of lightweight polymers. While using plastics does reduce the weight of the firearm a bit, they are still heavier than, say, recoil action firearms. On the other hand, the mechanism is very simple and easy to manufacture than a recoil action.

In the next few posts, we will study other blowback actions that use different ways of delaying the bolt assembly from moving backwards when the cartridge ignites.

Sunday, August 15, 2010

One of the variants of the Gardner Gun is an interesting weapon called the Bira gun. This was invented by a Nepalese General, Gehendra Shamsher Jang Bahadur Rana and named after the reigning Nepalese monarch of the time, King Prithvi Bir Bikram Shah. It has the distinction of being the last mechanically cranked machine gun ever manufactured.

The history of the Bira has to do with the political situation between Nepal and British India at that time. Under a Nepalese-British agreement, the Nepalese government allowed the British to trade with Nepal and Tibet and allow recruitment of Gurkhas in the British Indian army. In turn, the British agreed to sell firearms and ammunition and a wide variety of armaments to the Nepalese. However, despite Nepalese requests to purchase machine guns, the British declined to do so, because they feared that the Nepalese would clone these (which they already did with some other British origin firearms) and then they would have too many automatic weapons and could challenge British power in India.

Undaunted, the Nepalese set upon building their own machine gun design around 1896-97. Without a background in firearms design, it was decided to start by borrowing a design from somewhere else, in this case, a British model of the American Gardner machine gun. The firing mechanism was essentially the same as the Gardner gun, but there were some other significant differences.

The first difference is that the caliber of this weapon is different from the Gardner gun. Since the Nepalese had already built up a large supply of ammunition for Martini-Henry rifles, it was decided to make their machine gun use the same cartridges as the Martini-Henry (i.e.) the 0.577-450 cartridge.

Unlike the Gardner gun is that the Bira doesn't have a vertical magazine for holding ammunition. Instead, it uses an drum magazine mounted horizontally on top of the barrel. The flat circular drum magazine can be clearly seen in the picture above. The drum magazine could hold up to 120 rounds, in 60 rows of 2 rounds each, one on top of the other. The magazine weighs around 14 kg. when empty and about 19 kg. when fully loaded with ammunition.

Biras were mostly made of iron and steel parts, but the wheels were made of teak wood and brass was used for the wheels controlling the vertical elevation and horizontal traverse, as well as the gearing used for these.

The Bira has twin barrels very much like the Gardner gun, but there is no cooling water jacket around the barrels.

One more curious difference is that the crank is turned backwards (i.e. counter-clockwise) instead of forwards. This was done because the General opined that it was easier to pull instead of push and since pulling is a more natural movement, it is easier to operate the weapon for longer periods without fatigue.

Since Nepal did not have any modern factories during this time, each gun was hand-made. This meant that they could not interchange parts at all. In fact, in some cases, individual screws on a Bira were marked to fit in specific holes! Similarly, the magazines were also numbered to match the serial numbers of specific guns, since they were hand-fitted individually and would only fit in a particular gun. In the above picture, you can see the serial number plate of the gun: it is the oval yellow plate located between the crank and the drum magazine.

Due to the hand-made nature of manufacturing, only 50 or so Bira guns were ever manufactured. These were put into storage and none of them ever saw any wartime service. By then, the Maxim machine gun had been invented and the Bira became obsolete almost as soon as it was made. In the late 1970s, some Bira guns were put on sale in the market and acquired by collectors in the United States. When one was fired in 2009, it was found that it was still pretty accurate once the sights were dialed in. It was also found that in spite of one of the extractors of the gun being damaged, the gun could still fire due to its rugged design!

One of the earliest automatic weapons was the Gardner Gun, invented by one William Gardner of Toledo Ohio. Mr. Gardner had served on the Union side during the US Civil war and had witnessed the power of the Gatling gun. He soon came up with his own design of a machine gun in 1874 and made a hand-made prototype. Having no funding available to him, he sold the manufacturing rights to the newly formed firm of Pratt and Whitney of Hartford, Connecticut under the condition that they would pay him a royalty fee for every weapon sold. As we've seen before, Francis Pratt and Amos Whitney were two experienced engineers who had met when they both worked in Samuel Colt's firearms factory, inventing machines to manufacture firearms quickly. They set to work automating the process of building the Gardner gun and within a year, had turned it into a design that could be presented to a military selection committee.The design consists of a single or a twin barrel gun (such as the one shown above). The barrels are encased within an outer cylindrical jacket that can be filled with water, to prevent the barrels from overheating. A vertical magazine at the rear of the weapon contains cartridges ready to be loaded into the weapon. The hand crank on the side of the case operates the weapon. The barrels are loaded, fired and unloaded alternately with a single turn of the hand crank.

To facilitate faster loading, centerfire cartridges are placed into a wooden block with their rim ends protruding. The wooden block is moved so that the rim ends of the cartridges align with the feed slots (which are T-shaped) of the magazine. Then the wooden block is removed and leaves behind the cartridges with their rims inside the feed guide slots.

To fire the weapon, one man fills the feed slots with new ammunition and another one aims the weapon and turns the crank. As ammunition is used up, the first man can continue refilling the magazine from the top as needed.

A couple of improvements were made by Pratt and Whitney, which were not part of the original Gardner design: The feed system was improved using cams and levers to take a round and move it positively into place, instead of the earlier gravity feed. They also improved the extractor device and added features to cock the firing pin very slowly to prevent accidental discharges. They also added a safety mode that allowed users to run ammunition through the weapon without firing. An illustration of the firing mechanism is shown below.

The Gardner gun was demonstrated successfully to the US Navy board by Francis Pratt and Amos Whitney themselves. The Navy adopted this weapon and purchased a limited number of them. Unfortunately, the US Army was less interested in this weapon. However, a presentation made in front of the British Navy was much more successful and they bought a license to produce the gun in Europe. One of the major advantages of the Gardner gun over its rivals was that it was a lot lighter than its competitors (various Gatling gun models) and had a higher rate of fire. The British Navy purchase was soon followed by another British order for all branches of their military and they used the weapon in a few African wars in Sudan and the Upper Nile.

The first automatic action we will study is called the "Gatling action" named after an American, Dr. Richard Gatling, who invented the Gatling gun.

The predecessor of the Gatling gun was a multi-barreled weapon called the Mitrailleuse gun, the first variant of which was invented by a Belgian captain named Fafschamps in 1851. A number of different variations of Mitrailleuse guns were invented by many people, but some of the features remain common to all of them. They all have multiple barrels which can be loaded simultaneously. Turning a crank fires these barrels. Then the breech of the weapon is opened and the magazine plate is taken out and a new magazine plate containing more rounds is loaded into the breech.

The above two pictures show a Mitrailleuse type gun and one of its magazines from the 1850s. Such guns were often heavy and came mounted on a carriage for easy transportation.

One of the problems of such guns was that it was difficult to aim at range and also, the shots were not as dispersed as they had hoped. Hence, this type of gun was a failure on the battlefield, but its multi-barrel design inspired the Gatling Gun.

Ironically, Dr. Richard Gatling, who invented his weapon in 1861, hoped that his weapon would show how futile war is and reduce combat deaths that way. His invention was used in the US Civil war and soon adopted by other countries.

It consists of multiple rotating barrels which are turned by a hand crank. The original Gatling gun was fed by a hopper containing loose cartridges. The idea of a multi-barrel weapon was not new at this point, as the Mitrailleuse guns showed, as well as the pepperbox revolvers of the era. However, one of the innovations of the Gatling was that, as one barrel is being fired, the other barrels are simultaneously in various stages of either unloading or loading a cartridge. This means, even if there are only (say) six barrels in the weapon, the user doesn't have to stop and reload after six shots are fired. The Gatling automatically loads new cartridges from the hopper, as the crank turns. This allowed even unskilled soldiers to maintain high rates of fire. Indeed, a four man crew could shoot up to 1200 rounds per minute using a weapon like this.

The Gatling gun originally used paper cartridges, but soon adopted the newer metallic centerfire cartridge technology. Each barrel of a gatling gun fires once per revolution, at the exact same position. Each barrel has its own grooved carrier and lock mechanism. Each barrel also has a cam that forces the lock to move in a back and forth reciprocating motion. When the crank is turned, cartridges from a gravity-fed hopper drop into the grooved carriers. The lock is forced forward by the cam and loads the cartridge. At the highest point of the cam, the lock releases and fires the cartridge. Then the cam keeps turning and opens the lock to eject the spent cartridge to the ground.

The Union army of the United States was the first to adopt the Gatling Gun into service. Its effectiveness was actually demonstrated by a salesman in a live combat situation! Soon afterwards, it was adopted by many other countries as well.

The Gatling gun mainly fell out of favor because of its weight and because it had to be transported on a carriage. However, in the 1950s, the concept of a multi-barrel firing weapon made a comeback and the Gatling style design is still being used by combat aircraft such as the A-10 Warthog, to this present day. In its modern descendants, the barrels are turned by the action of an electric motor rather than a hand crank.

The advantage of a Gatling-style gun is that since multiple barrels are used, it can be used for continuous and high rates of fire. For instance, if a gun has 10 rotating barrels, it can safely be fired at a rate of say 1000 rounds per minute., since each barrel only fires 100 rounds per minute individually. This allows each barrel to sufficiently cool before loading a new round. By contrast, a single barrel weapon would start to overheat at these firing rates and its barrel could jam or distort due to the heat.

In the actions we've studied earlier, such as bolt-action, lever action, pump action etc., the user has to fire the weapon and then manipulate some lever manually, in order to eject the old spent cartridge and load in a new cartridge. In many cases, these weapons have multiple cartridges loaded into the magazine and manipulating the lever strips a new cartridge from the magazine.

In the case of revolvers, the act of pulling back the hammer or the trigger rotates the cylinder and brings upon a new round to be fired.

In the early 1850s, it was realized that if the loading operation could be automated, then this would lead to more rapidly firing firearms. This lead to several innovations in firearms technology. We will study some of the principal actions in the next few posts, such as the Gatling action, chain action, blowback action, gas operated action, recoil action etc.

This might be a good stage to gloss over the differences in various actions:

Gatling: This consists of a multiple barrel weapon. The various barrels rotate about a central axis and fire one at a time. The barrels may be rotated by hand or by an electric motor.

Chain driven: This is a single barrel weapon that uses a electric motor and a drive chain to drive the mechanisms to load a cartridge, fire it and eject the spent cartridge.

Blowback: In this type of mechanism, some of the expanding gases from a fired cartridge push back on the cartridge. The bolt holding the cartridge in place is not locked and is only held by spring pressure. The spent cartridge case is pushed back against the bolt and these are together forced back against the spring pressure and this force helps eject the old cartridge, cock the weapon and load a new cartridge into place. The barrel of a blowback weapon is generally fixed and does not move when the weapon is fired.

Gas operated: In this type of action, as the gas escapes through the front of the barrel, some of it is bled off and fed back to actuate the ejection of the spent cartridge and load a new one.

Recoil operated: In this type, the bolt and barrel are locked at the point that the cartridge is fired (a key difference from the blowback action where the bolt is never locked.) After the cartridge is fired, the barrel and bolt move together in the opposite direction from the bullet, due to Newton's third law of motion. The barrel stops moving at one point and the bolt unlocks and continues to move backward to cock the weapon, eject the old cartridge and load a new cartridge.

Blowback actions are generally used many smaller pistols and recoil operated weapons on some bigger pistols and shotguns. Gas operated mechanisms are generally used for assault rifles and some pistols. Gatling and chain actions are now generally used for larger fully automatic weapons, most of which are too heavy to be carried by a single individual and fall somewhat out of the range of what can be called "firearms".

Monday, August 9, 2010

We will now look at some coating treatments which are usually applied on top of some of the other treatments we studied previously to give it additional resistance to corrosion.

The first treatment we will look at is Teflon coating. Teflon was originally invented by DuPont in 1938 and is one of the slipperiest substances in the world. It is used to coat non-stick pots and pans in the kitchen, but is also used in industries like aerospace, electronics, architecture and now, firearms as well. Teflon can be applied on top of stainless steel parts, blued parts and metals like titanium and aluminum. A Teflon coat has more resistance to wear than bluing. It is also completely weatherproof and prevents rust from forming by preventing any humidity from reaching the metal underneath. After a teflon coat is applied, there is no need to oil the gun further as teflon is self lubricating and only gets more slipperier as it wears down. This means that there is no chance of the oil in the gun freezing in cold temperatures. Cleanup is also simple because all it takes is an air hose and a quick wipe down. It also comes in a few different colors, so if the user desires to have a black or a camouflage coating applied to a bright stainless steel barrel, it is possible to simply apply a teflon coat to take care of this.

The above is an All Weather Pistol manufactured by C.O. Arms. It is made of SAE 4140 carbon steel and aluminium and is coated with teflon. In this example, the firearm is coated black.

The above is a Colt Defender with a stainless steel slide and teflon coating. The teflon coat is clear in this example.

Another coat is called KG Gun Kote, which was invented by KG Industries LLC. This was originally designed to the specifications of the US Navy's SEAL team 1. The requirement was for a coat that would withstand at least 500 hours of a standard salt spray test (5% salt solution sprayed continuously in a chamber) and still meet the military machine gun firing requirements. Gun Kote is a phenolic resin that is designed to be applied by spraying on or dip spin. It is then thermally cured at temperatures between 300-325 F. The resulting coat is only 0.0003-0.0005 inches thick, but is tougher than bluing or parkerizing and has a pencil hardness greater than 9H. It is abrasion resistant, chemical and corrosion resistant and has lubricity. The lubrication is produced by molybdenum disulfide. Gun Kote has also been tested against a number of chemicals ranging from sulfuric acid to hydraulic oil and successfully resisted them all. One version not only passed the 500 hour salt-spray test, it actually lasted over a 1000 hours with no problems! The South African military tested it on an equivalent of a 7 year corrosion test, which it also passed. Like the teflon coat, it also comes in a number of colors. Since the original product, they have come up with a number of different formulations. Many manufacturers such as Kimber, Buzztail etc. use KG Gun Kote and it can be applied to other vendors products by third party gunsmiths as well.

Colt 1911 pistol coated with Gun Kote

Another coating treatment is Duracoat by Lauer Custom Weaponries. It is an extremely hard polymer, which is resistant to oil and cleaning chemicals. It is also somewhat self-lubricating. Duracoat hardness is between H than 2H pencil hardness and it has good impact resistance as well. It can easily pass a 300 hour salt spray test. It can be applied to almost any surface (metal, plastic, wood) as long as proper preparation of the surface and pre-treatment is done. The substance is quick drying -- it is dry to the touch in 20 minutes and the weapon can be used in 6-8 hours. It continues to cure for 4-6 weeks afterwards though. Duracoat is available in a very wide range of colors (over 130 standard colors and 11 standard camouflage patterns). One of the very good advantages of Duracoat is that it is very temperature resistant and can easily withstand over 1800 degrees F. Therefore, it is an excellent choice for weapons with a high sustained rate of fire, such as LMGs or fully-automatic rifles.

Glock pistol coated with neon pink duracoat :D

FN rifle painted with camouflage duracoat colors.

Another coating treatment is CeraKote invented by NIC industries. This is a ceramic based coating and comes in two types: "C" series, which cures in normal temperatures and "H" series, which is a thermal cure coating. Cerakote offers very good abrasion resistance, corrosion resistance and hardness. Because of its ceramic base, it is harder and over 60% more wear-resistant than teflon. Since it is also self-lubricating, a firearm requires very little oil on top of it. The C series has a pencil hardness of 7H and can withstand over 550 hours of standard salt spray test. It can also withstand over 1200 degrees F over extended periods of time without failing, which makes it very suitable for weapons with high rates of fire. The "H" series can pass 2500 hours of salt spray test and withstand 550 F temperature for extended periods of time. It comes in 31 colors.